With rapid development of the global economy, the depletion of fossil fuels and increasing environmental pollution, advanced technologies for energy conversion and storage are being extensively studied around the world. Rechargeable lithium-ion batteries have been regarded as one of the most efficient and environmentally benign types of energy storage devices and are widely utilized in various portable electronic devices, hybrid electric vehicles and emerging smart grids. Carbon materials as electrode materials of lithium-ion batteries have been predominantly used and are commercially viable for industrialization because of their low cost, easy accessibility and processability. An example of such carbon materials is graphite.
However, one problem with utilizing graphite is that it suffers from low energy density (theoretical capacity 372 mA h g−1) when used as an anode material for lithium-ion batteries. To better satisfy the ever-growing demand for high-performance power sources, the development of nanostructured carbon materials (such as graphene, carbon nanotubes, fullerenes, etc.) with high conductivity and accessible specific surface area has attracted great research interest in the last decade.
Nanocarbons have been considered as promising electrode materials for the next generation of lithium-ion batteries. However, one problem with present commercial carbon nanomaterials is that they are mostly fabricated from non-renewable resources (such as coals and petroleum) or relatively expensive polymers (such as polyacrylonitrile (PAN) and phenolic resins). However, energy shortages and growing market demands still necessitate a need to find cost-effective, environmentally benign and renewable sources for producing high performance nanocarbon materials.
Another problem with present commercial carbon nanomaterials is that they may require complicated and expensive fabrication processes which may not be suitable for large-scale applications.
Another problem with present commercial carbon nanomaterials when used in an electrode material for energy storage devices is that they may be unstable when used in different electrolytes and may not perform well in a wide range of temperatures.
A further problem with present commercial carbon nanomaterials is that they may not be free-standing without using a binding agent. Most commercially available carbon electrode materials are in powder form and are typically mixed with a binding agent (for example, polyvinylidene fluoride) during the fabrication process. The use of a binding agent may disadvantageously result in a tedious fabrication process and poorer electrochemical performance. Furthermore, the use of a binding agent may contribute substantially to the overall cost of fabrication.
There is therefore a need to provide conductive materials that overcome, or at least ameliorate, one or more of the disadvantages described above.
There is a need to provide conductive materials that may be fabricated from low-cost, abundant, environmentally benign and renewable materials.
There is a need to provide conductive materials useful in electrode materials for lithium-ion batteries that exhibit high specific capacity.
There is a need to provide conductive materials that are easily processable, have large accessible surface area, high carbon purity, high electrical conductivity and high structural integrity.
There is a need to provide conductive materials that may be fabricated through conventional and straightforward processes which may be conducted on a large commercial scale.
There is a need to provide conductive materials are stable when used in different electrolytes and perform well in a wide range of temperatures when used in an electrode material for energy storage devices.
There is a need to provide conductive materials that are free-standing without using any binding agent, thereby simplifying the fabrication process and reducing its overall cost.